The present disclosure relates to a semiconductor device, and more particularly to a semiconductor device having an embedded pad structure.
Along with the miniaturization of semiconductor devices, the damascene process has been increasingly used for formation of interconnect structures.
FIG. 13A is a plan view of a semiconductor device of the first conventional example, and FIG. 13B is a cross-sectional view taken along line A-A in FIG. 13A.
As shown in FIGS. 13A and 13B, insulating layers 18, 26, and 27 are formed sequentially on a semiconductor substrate (not shown). A bonding pad 21 is embedded in the insulating layer 27 with a barrier metal 20a interposed between the bonding bad 21 and the insulating layer 27. Although illustration is omitted, an uppermost interconnect electrically connected to the bonding pad 21 is formed in the insulating layer 27, and a via is formed in the insulating layers 18 and 26 for connection between the uppermost interconnect and a lower interconnect. An insulating layer 22 is formed on the insulating layer 27 and the bonding pad 21. The insulating layer 22 has an opening 23 to expose the top surface of the bonding pad 21.
A chemical mechanical polishing (CMP) technique is used for formation of the bonding pad 21 in the damascene process. However, using the CMP technique, the bonding pad 21 tends to be etched excessively at its center, as shown in FIG. 13B, causing dishing where the bonding pad 21 is dented like a dish.
FIGS. 14A and 14B show how the dishing occurs in the semiconductor device of the first conventional example. As shown in FIG. 14A, after formation of a groove 19b in the insulating layer 27, the barrier metal 20a is formed on the insulating layer 27 to cover the walls and bottom of the groove 19b, and thereafter a metal film 21′ is formed on the barrier metal 20a to fill the groove 19b. Thereafter, as shown in FIG. 14B, portions of the metal film 21′ and barrier metal 20a existing outside the groove 19b are removed by CMP. During this removal by CMP, the metal film 21′ is etched, not only mechanically, but also chemically. Therefore, when the bonding pad 21 having a size of about 100 μm×100 μm is to be formed by leaving the portion of the metal film 21′ in the groove 19b unremoved, the center of the portion of the metal film 21′ in the groove 19b tends to be etched excessively by chemical etching mainly, causing dishing.
In view of the above problem, a technique of forming a pad structure using the damascene process while preventing occurrence of dishing is proposed (see Japanese Unexamined Patent Application Publication No. H10-64938).
FIG. 15A is a plan view of a semiconductor device of the second conventional example disclosed in Japanese Unexamined Patent Application Publication No. H10-64938, and FIG. 15B is a cross-sectional view taken along line A-A in FIG. 15A.
As shown in FIGS. 15A and 15B, insulating layers 18, 26, and 27 are formed sequentially on a semiconductor substrate (not shown). A bonding pad 21 is embedded in the insulating layer 27 with a barrier metal 20a interposed between the bonding bad 21 and the insulating layer 27. The bonding pad 21 in this example has a lattice shape for prevention of dishing during CMP. Although illustration is omitted, an uppermost interconnect electrically connected to the bonding pad 21 is formed in the insulating layer 27, and a via is formed in the insulating layers 18 and 26 for connection between the uppermost interconnect and a lower interconnect. An etching stopper layer 29 and an insulating layer (passivation layer) 22 are formed on the insulating layer 27 and the bonding pad 21. The etching stopper layer 29 is made of a material that allows selective etching against the materials of the insulating layer 27 and the passivation layer 22. The etching stopper layer 29 and the passivation layer 22 have an opening 23 to expose the top surface of the bonding pad 21.
In the semiconductor device of the second conventional example shown in FIGS. 15A and 15B, which has the lattice-shaped bonding pad 21, no excessive etching occurs in any portion of the bonding pad 21 formed using the CMP technique. Thus, dishing can be effectively prevented.